Variable Preemption in Time Sensitive Networks Using Priority Regeneration

ABSTRACT

A method for operating a time-sensitive network, TSN, having a first, high-importance segment and a second, low-importance segment, includes remapping, using TSN per-port priority regeneration, priority labels attached to data streams received on the first port and the second port to updated priority labels; splitting the data streams into a “preempting” class and a “preemptable” class based on a mapping from updated priority labels to classes; and forwarding the data streams from a border network element to at least one next-hop network element. When congestion is present on a link to the next-hop network element, the forwarding of “preempting” data streams takes precedence over the forwarding of “preemptable” data streams.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims priority to European Patent ApplicationNo. 21182035.2, filed on Jun. 28, 2021, which is incorporated herein inits entirety by reference.

FIELD OF THE DISCLOSURE

The present disclosure relates to the field of time sensitive networks,TSN, that may, for example, be used as a communication medium indistributed control systems, DCS, in industrial plants.

BACKGROUND OF THE INVENTION

Distributed control systems, DCS, for an industrial plant comprises aplurality of controllers, sensors and actuators. Sensors may, forexample, deliver measurement values from within an industrial processbeing executed on the plant. A controller may then, for example,communicate with actuators that physically act upon the process with thegoal of keeping the measurement value (such as a temperature or apressure) at a desired set-point value.

Communication within the DCS requires a fast and reliable delivery ofdata streams. Dedicated field bus networks are designed to provide therequired low latency and reliability, but it is intended to replacemultiple proprietary field bus systems with a standardized highperformance network. For this purpose, time sensitive networks, TSN,that build upon traditional Ethernet networks are well-known in the art.WO 2020/136 487 A2 discloses a controller for process plants that isable to communicate in a network with a mixture of TSN devices andnon-TSN devices.

Configuration of a TSN as a whole may be quite complex andtime-consuming depending on the number of participants.

BRIEF SUMMARY OF THE INVENTION

In a general aspect, the present disclosure describes a system andmethod for facilitating facilitate, and permitting a partial automationof, the configuration of a TSN.

This objective is achieved by a method for operating a TSN according toa first independent claim and by a method for configuring a TSNaccording to a second independent claim. Further advantageousembodiments are detailed in the respective dependent claims.

In one embodiment, the disclosure describes a method for operating atime sensitive network, TSN. This TSN comprises at least a first,high-importance segment and a second, low-importance segment. The terms“high-importance” and “low-importance” are relative terms with respectto the concrete application at hand. In every application, there will besome data streams whose timely and reliable delivery is more criticalthan the delivery of other data streams. For example, a measurementvalue that is captured somewhere in an industrial process and is merelydisplayed somewhere in the control room is still important to somedegree (otherwise it would not be measured in the first place). But theupdating of this measurement value is less time-critical than theupdating of a measurement value that is part of a closed feedback loop.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

In the following, the invention is illustrated using Figures without anyintention to limit the scope of the invention.

FIG. 1 illustrates an exemplary embodiment of a method for operating aTSN in accordance with the disclosure.

FIG. 2 illustrates an exemplary network geometry having acongestion-prone segment, in accordance with the disclosure.

FIG. 3 illustrates an exemplary embodiment of a method for configuring aTSN in accordance with the disclosure.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic flow chart of an embodiment of the method 100 foroperating the TSN 1. As it will be shown in FIG. 2 in more detail, theTSN 1 comprises network elements 3 a-3 i, 4 that are interconnected byphysical links 2 a-2 i. The TSN 1 comprises a first, high-importancesegment 1 a with network elements 3 a-3 b and a second, low-importancesegment 1 b with network elements 3 c-3 e.

In step 110, on the network elements 3 a-3 e in segments 1 a and 1 b,data streams 5 a-5 g that carry priority labels 6 a-6 g are split into a“preempting” class 7 a and a “preemptable” class 7 b based on a mappingfrom the priority labels 6 a-6 g to classes 7 a, 7 b that is configuredseparately for each segment 1 a, 1 b.

In step 120, the data streams 5 a-5 g are forwarded to respectivenext-hop network elements 3 a-3 e, 4, wherein the forwarding of datastreams 5 a-5 g in the “preempting” class 7 a takes precedence over theforwarding of data streams 5 a-5 g in the “preemptable” class 7 b.

In step 130, the border network element 4 employs TSN per-port priorityregeneration to remap priority labels 6 a-6 g attached to data streams 5a-5 g received on the first port 4 a and the second port 4 b to updatedpriority labels 6 a*-6 g*. This remapping is performed such that no datastream 5 a-5 c originally received on the first port 4 a has the sameupdated priority label 6 a*-6 g* as any data stream 5 d-5 g originallyreceived on the second port 4 b.

In step 140, on the border network element 4, the data streams 5 a-5 gare split into a “preempting” class 7 a and a “preemptable” class 7 bwith respect to the forwarding on to a next-hop network element 8. Thissplitting is based on a mapping from updated priority labels 6 a*-6 g*to classes 7 a, 7 b that is configured on the border network element 4.

According to block 141, on the border network element 4, memory may beallocated for the queuing of frames of received data streams 5 a-5 gsuch that queues for frames of “preemptable” data streams 5 a-5 g areable to accommodate more frames than queues for frames of “preempting”data streams 5 a-5 g. According to block 141 a, the sizes of the queuesmay be made dependent also on the updated priority labels 6 a*-6 g* ofthe data streams 5 a-5 g.

In step 150, the data streams 5 a-5 g are forwarded from the bordernetwork element 4 to at least one next-hop network element 8. At leastin case of congestion on a link 2 f to the next-hop network element 8,the forwarding of data streams 5 a-5 g in the “preempting” class 7 atakes precedence over the forwarding of data streams 5 a-5 g in the“preemptable” class 7 b.

In step 160, the next-hop network element 8 may optionally restore theoriginal priority labels 6 a-6 g.

FIG. 2 shows an exemplary network geometry of a TSN 1. The TSN 1comprises network elements 3 a-3 i, 4 that are interconnected byphysical links 2 a-2 i. Network elements 3 a and 3 b with links 2 a and2 b form a first, high-importance segment 1 a. Network elements 3 c, 3 dand 3 e with links 2 c, 2 d and 2 e form a second, low-importancesegment 1 b. The first segment 1 a produces data streams 5 a-5 c withpriority labels 6 a-6 c. The second segment 1 b produces data streams 5d-5 g with priority labels 6 d-6 g.

Both segments 1 a and 1 b are connected to the border network element 4.The first segment 1 a is connected to a first port 4 a, and the secondsegment 1 b is connected to a second port 4 b of the network element 4.The border network element 4 remaps the priority labels 6 a-6 g toupdated priority labels 6 a*-6 g* and forwards all data streams 5 a-5 gto the next-hop network element 3 g, 8 to which it is connected via athird port 4 c. Since all the data streams 5 a-5 g have to travel acrossone single physical link 2 f between the border network element 4 andthe next-hop network element 8, the segment 1 c comprising the bordernetwork element 4, the next-hop network element 8 and the physical link2 f is a congestion-prone segment.

When the next-hop network element 3 g, 8 forwards the data streamsfurther on to other network elements 3 f and 3 i, it does so viamultiple links 2 g, 2 i, so there is less propensity for a congestion ofone of those links 2 g, 2 i.

FIG. 3 is a schematic flow chart of the method 200 for configuring theTSN 1, e.g., the TSN 1 shown in FIG. 2 .

In step 210, at least one segment 1 c of the TSN 1 is identified thatprovides connectivity to or from at least a first further segment 1 aand a second further segment 1 b of the TSN 1. That is, a constellationof the first further segment 1 a, the second further segment 2 b, andthe segment 1 c that is needed by both segments 1 a and 1 b, isidentified. As discussed before, the segment 1 c is a congestion-pronesegment because simultaneous high traffic going into and/or out or bothsegments 1 a and 1 b may overload it.

In step 220, a network element 4 that is connected to the first furthersegment 1 a by a first port 4 a, to the second further segment 1 b by asecond port 1 b, and to the congestion-prone segment 1 c by a third port4 c, is identified as a border network element 4.

In step 230, the border network element 4 is configured to: remap, usingTSN per-port priority regeneration, priority labels 6 a-6 g attached todata streams 5 a-5 g received on the first port 4 a and the second port4 b to updated priority labels 6 a*-6 g*, such that no data stream 5 a-5g originally received on the first port 4 a has the same updatedpriority label 6 a*-6 g* as any data stream 5 a-5 g originally receivedon the second port 4 b; split the data streams 5 a-5 g into a“preempting” class 7 a and a “preemptable” class 7 b based on a mappingfrom updated priority labels 6 a*-6 g* to classes 7 a, 7 b; and forwardthe data streams received on the first port 4 a and the second port 4 bto the third port 4 c. The forwarding of data streams 5 a-5 g in the“preempting” class 7 a takes precedence over the forwarding of datastreams 5 a-5 g in the “preemptable” class 7 b.

In step 240, at least one key performance indicator 1* of the TSN 1 ismonitored and/or simulated.

In step 250, the remapping of the priority labels 6 a-6 g, and/or thesplitting of the data streams 5 a-5 g into the “preempting” class 7 aand the “preemptable” class 7 b, is optimized with the goal of improvingthe key performance indicator 1*.

In the embodiments described herein, the segments are independent inthat traffic within the first segment on the one hand and traffic withinthe second segment on the other hand pass through different sets ofphysical links in the TSN. The first segment and the second segment areconnected by a border network element. The first segment is connected toa first port of the border network element, and the second segment isconnected to a second port of the border network element. By means of athird and more ports, the border network element may connect the firstand second segment to the outside world, i.e., further segments of theTSN, or the Internet.

Data streams received on the first port and the second port havepriority labels attached to them. These priority labels may, forexample, Time-Aware Traffic Shaping, TAS, priorities. According to theTSN standard, there are eight different TAS priorities. In the course ofthe method, the border network element remaps these priority labels toupdated priority labels such that no data stream originally received onthe first port has the same updated priority label as any data streamoriginally received on the second port.

The border network element splits the data streams into a “preempting”class and a “preemptable” class based on a mapping from updated prioritylabels to classes. For example, if there are 8 priority levels from 0 to7, priority levels 7 to 4 may be mapped to the “preempting” class, andpriority levels 3 to 0 may be mapped to the “preemptable” class.

The border network element forwards the data streams to at least onenext-hop network element. At least in case of congestion on a link tothe next-hop network element, the forwarding of “preempting” datastreams takes precedence over the forwarding of “preemptable” datastreams. That is, frames of “preemptable” data streams may have to waitin a queue to be transmitted until transmission of frames belonging to“preempting” data streams is finished.

The first and second network segments may be managed independently. Thismeans that a first data stream in the first network segment may beassigned a particular priority label (e.g., 5), and a second data streamin the second network segment may be assigned the same priority label.After the remapping, the two data streams will have different updatedpriority labels. Thus, at the time of splitting into the “preempting”and “preemptable” classes, the updated priority labels reflect that thefirst data stream is more important than the second data stream becauseit originates from the more important first network segment.Consequently, the first data stream may be mapped to the “preempting”class, and the second data stream may be mapped to the “preemptable”class, so that the first data stream is delivered with a betterdeterminism at the expense of the second data stream.

On top of the condition that no data stream originally received on thefirst port has the same updated priority label as any data streamoriginally received on the second port, the remapping and the subsequentsplitting may proceed according to any suitable set of rules that takeinto account the importance of each data stream with respect to theapplication at hand.

In one simple example, all data streams from the first, high-importancesegment may be assigned updated priority labels that will cause them tobe mapped to the “preempting” class during the splitting, whereas alldata streams from the second, low-importance segment may be assignedupdated priority labels that will cause them to be mapped to the“preemptable” class during the splitting.

In another example, the remapping may raise the priority labels of datastreams from the first segment and lower the priority labels of datastreams from the second segment. During the splitting, all data streamswith a priority label above a predetermined threshold may then be mappedto the “preempting” class, whereas the data streams with a prioritylabel below this threshold may be mapped to the “preemptable” class. Inthis manner, the original priority labels of the data streams, whichreflect their relative prioritization within the respective networksegments, still have some bearing on the final decision whether thesedata streams will be mapped to “preempting” or “preemptable”.

Thus, the prioritization within each network segment and the processingon the border network element may work hand in hand to improve thedeterminism with which system-important traffic is conveyed through theTSN. But an improvement of this determinism may also be achieved if anexisting TSN is taken as it is and only the processing on the bordernetwork element is modified. That is, the determinism may also beimproved by making only changes in one single place. One advantage ofmaking a change in only one place is that an existing, tried-and-testedprioritization and configuration within the individual network segmentscan remain as it is. In some high-risk applications, such as chemical ornuclear processes, any configuration change may be dependent on priorregulatory approval. It is far easier to get such approval for a changethat only affects the border network element, and thus leavescommunication within each network segment as it is, than to get it for acomplete redesign of the TSN.

In an advantageous embodiment, the next-hop network element may restorethe original priority labels of the data streams. In this manner, theeffect of the remapping may be limited to the link between the bordernetwork element and the next-hop network element. For example, theremapping and the splitting on the border network element may bespecifically used to relieve a congestion on a link between the bordernetwork element and the next-hop network element that is a bottleneckwithin the TSN, but once this bottleneck has been passed, the originalprioritization information may be re-used. For example, a link betweenthe border network element and the next-hop network element may becomebottleneck-prone if it has to carry traffic to or from several networksegments and it has a lesser bandwidth than the combined bandwidths ofsaid several network segments.

In a further advantageous embodiment, data streams may already be splitinto a “preempting” class and a “preemptable” class on network elementsin the first and second segments. These network elements may thenforward the data streams to respective next-hop network elements suchthat, at least in case of congestion on a link to the respectivenext-hop network element, the forwarding of “preempting” data streamstakes precedence over the forwarding of “preemptable” data streams. Themappings from priority labels to classes differ between the first andsecond segments. That is, there is a segment-wise preemptionconfiguration. In this context, the combination of the remapping and thesplitting on the border network element according to the present methodpermits to use the TSN preemption mechanism on the uplink from theborder network element to the outside world, while leaving the existingpreemption configuration in the individual network segments intact. Butthere may also be any degree of coordination and cooperation between theconfigurations of the individual network segments and the configurationof the border network element.

In one example, the mapping between priority labels and classes withinthe first and/or second network segment, the remapping of prioritylabels on the border network element, and the mapping from updatedpriority labels to classes on the border network element, may becoordinated such that no data stream that is in the “preemptable” classwithin the first and/or second network segment is in the “preempting”class upon forwarding from the border network element. In this manner,it is avoided that a privileged handling of a data stream by the bordernetwork element “goes to waste”: By virtue of having been in the“preemptable” class in its originating network segment before reachingthe border network element, it is already “tainted” withnon-determinism. Transmission of this data stream can no longer be madehighly deterministic by privileged handling on the border networkelement.

In another example, the mapping between priority labels and classeswithin the first and/or second network segment, the remapping ofpriority labels on the border network element, and the mapping fromupdated priority labels to classes on the border network element, arecoordinated such that at least one system-important data stream is inthe “preempting” class both within the first and/or second networksegment and upon forwarding from the border network element. In thismanner, this particular system-important data stream may be transportedthrough the whole TSN in a highly deterministic manner. The privilegedhandling of the data stream in its originating network segment is not“wasted” by virtue of a non-deterministic handling on the border networkelement.

As discussed before, the TSN may be chosen to comprise controllers,sensors and actuators of a distributed control system, DCS, for anindustrial plant as participants. In this manner, the TSN may take theplace of a previous proprietary field bus network without sacrificingthe determinism.

In the context of a DCS, at least one data stream that is part of aclosed feedback loop of an industrial process may be chosen as asystem-important data stream. Transmission of such data-streams istime-critical because an undue delay may cause the process to escalatebeyond control. For example, a pressure in a vessel may rise beyond thephysical limits of the vessel in a very short time if the measurementvalue of this pressure is delayed in the network and does not reach thecontroller in time to react, or if the command from the controller toopen a relief valve is lost in the network and this valve is not opened.

In a further advantageous embodiment, memory for the queuing of framesof received data streams is allocated on the border network element suchthat queues for frames of “preemptable” data streams are able toaccommodate more frames than queues for frames of “preempting” datastreams. The border network usually stores received frames of datastreams in a queue and forwards them according to the“first-in-first-out” (FIFO) principle. For example, there may be onequeue per possible priority label. If there is congestion and one“preemptable” data stream has to wait for another “preempting” datastream, the queue for that priority label may fill up. Once the queue isfull, either newly arriving frames for this queue may be dropped, orthese newly arriving frames may cause the oldest frames at the front ofthe queue to be dropped. The larger the queue, the lesser theprobability that data is lost in this manner. If there is a limitedamount of queue space to work with, then it is advantageous toconcentrate this on data streams that have a higher propensity of beingleft waiting. By contrast, highly prioritized “preempting” data streamsdo not need a large queue because the frames will not be waiting therefor long. The sizes of the queues may furthermore be made dependent alsoon the updated priority labels of the data streams, which are a furtherindicator of the probability that frames of a particular data streamwill have to wait to be transmitted.

The present disclosure also describes a method for configuring a timesensitive network, TSN. This TSN comprises a plurality of networkelements that are interconnected by links. The network elements areconfigured to forward data streams to respective next-hop networkelements.

The method starts with identifying at least one segment of the TSN thatprovides connectivity to or from at least a first further segment and asecond further segment of the TSN as a congestion-prone segment. Inparticular, if the available bandwidth in this segment is less than thecombined bandwidths of the first and second further segments,simultaneous high activity in both further segments may overload thecongestion-prone segment.

Next, a network element that is connected to the first further segmentby a first port, to the second further segment by a second port, and tothe congestion-prone segment by a third port, is identified as a bordernetwork element. This border network element is then configured to:remap, using TSN per-port priority regeneration, priority labelsattached to data streams received on the first port and the second portto updated priority labels, such that no data stream originally receivedon the first port has the same updated priority label as any data streamoriginally received on the second port; split the data streams into a“preempting” class and a “preemptable” class based on a mapping fromupdated priority labels to classes; and forward the data streamsreceived on the first port and the second port to the third port,wherein the forwarding of “preempting” data streams takes precedenceover the forwarding of “preemptable” data streams.

In this manner, as discussed above, the TSN network is improved in thatdata streams from a more important network segment may take precedenceover other data streams on the congestion-prone segment even if they areboth labelled as “important” in the context of the respective first andsecond further network segments.

The configuration may be performed in a fully automatic manner. Theinformation about the geometry of the network is typically available inelectronic form and may be parsed by machine. The border network elementmay be configured by software. No manual engineering of the TSN as awhole is required, whereas any engineering that has already gone intothe individual further network segments is preserved.

In a further advantageous embodiment, at least one key performanceindicator of the TSN is monitored and/or simulated. The remapping of thepriority labels, and/or the splitting of the data streams into the“preempting” class and the “preemptable” class, is then optimized withthe goal of improving the key performance indicator. For example, aplurality of candidate configurations of the remapping and/or thesplitting may be set up, and for each such candidate configuration, thekey performance indicator may be computed. A candidate configurationwith the best value of the key performance indicator may then beimplemented on the border network element.

In particular, the key performance indicator may comprise one or moreof: a data throughput in the congestion-prone network segment; a latencyof delivery of at least one data stream; a rate of frame loss of atleast one data stream; and a measure for determinism of delivery of atleast one data stream.

The optimizing for one or more key performance indicator may again beperformed in a fully automatic manner. Thus, the fine-grained breakdownof the priority of data streams into 8 different priority labels as perthe current TAS feature is no longer tied to a requirement for moremanual configuration of the TSN as a whole. There is no longer a choiceto be made between eight priorities and much manual configuration, oronly two preemption classes and less manual configuration.

The methods may be wholly or partially computer-implemented. Theinvention therefore also provides one or more computer programs withmachine readable instructions that, when executed on one or morecomputers, cause the one or more computers to perform one of the methodsdescribed above. In particular, a virtualization platform and one ormore hardware controllers may be regarded as computers.

The disclosure also describes one or more non-transitory storage mediaand/or download products with the one or more computer programs. Adownload product is a product that may be sold in an online shop forimmediate fulfillment by download. The invention also provides one ormore computers with the one or more computer programs, and/or with theone or more non-transitory machine-readable storage media and/ordownload products.

LIST OF REFERENCE SIGNS

1 time sensitive network, TSN

1 a first, high-importance segment of TSN 1

1 b second, low-importance segment of TSN 1

1 c congestion-prone segment of TSN 1

1* key performance indicator of TSN 1

2 a-2 i physical links of TSN 1

3 a-3 i network elements in TSN 1

4 border network element in TSN 1

4 a-4 c ports of border network element 4

5 a-5 g data streams

6 a-6 g priority labels of data streams 5 a-5 g

6 a*-6 g* updated priority labels produced by border network element 4

7 a “preempting” class for data streams 5 a-5 g

7 b “preemptable” class for data streams 5 a-5 g

8 next-hop network element

100 method for operating TSN 1

110 splitting data streams 5 a-5 g into classes 7 a, 7 b in segments 1a, 1 b

120 forwarding data streams 5 a-5 g within segments 1 a, 1 b

130 remapping priority labels 6 a-6 g on border network element 4

140 splitting data streams 5 a-5 g into classes 7 a, 7 a based on newlabels 6 a*-6 g*

141 allocating queue memory based on class 7 a, 7 b

141 a allocating queue memory based on new labels 6 a*-6 g*

150 forwarding data streams 5 a-5 g to next-hop network element 8

160 restoring original priority labels 6 a-6 g

200 method for configuring TSN 1

210 identifying congestion-prone segment 1 c serving segments 1 a, 1 b

220 identifying border network element 4

230 configuring border network element 4

240 monitoring and/or simulating key performance indicator 1*

250 optimizing with the goal of improving key performance indicator 1*

All references, including publications, patent applications, andpatents, cited herein are hereby incorporated by reference to the sameextent as if each reference were individually and specifically indicatedto be incorporated by reference and were set forth in its entiretyherein.

The use of the terms “a” and “an” and “the” and “at least one” andsimilar referents in the context of describing the invention (especiallyin the context of the following claims) are to be construed to coverboth the singular and the plural, unless otherwise indicated herein orclearly contradicted by context. The use of the term “at least one”followed by a list of one or more items (for example, “at least one of Aand B”) is to be construed to mean one item selected from the listeditems (A or B) or any combination of two or more of the listed items (Aand B), unless otherwise indicated herein or clearly contradicted bycontext. The terms “comprising,” “having,” “including,” and “containing”are to be construed as open-ended terms (i.e., meaning “including, butnot limited to,”) unless otherwise noted. Recitation of ranges of valuesherein are merely intended to serve as a shorthand method of referringindividually to each separate value falling within the range, unlessotherwise indicated herein, and each separate value is incorporated intothe specification as if it were individually recited herein. All methodsdescribed herein can be performed in any suitable order unless otherwiseindicated herein or otherwise clearly contradicted by context. The useof any and all examples, or exemplary language (e.g., “such as”)provided herein, is intended merely to better illuminate the inventionand does not pose a limitation on the scope of the invention unlessotherwise claimed. No language in the specification should be construedas indicating any non-claimed element as essential to the practice ofthe invention.

Preferred embodiments of this invention are described herein, includingthe best mode known to the inventors for carrying out the invention.Variations of those preferred embodiments may become apparent to thoseof ordinary skill in the art upon reading the foregoing description. Theinventors expect skilled artisans to employ such variations asappropriate, and the inventors intend for the invention to be practicedotherwise than as specifically described herein. Accordingly, thisinvention includes all modifications and equivalents of the subjectmatter recited in the claims appended hereto as permitted by applicablelaw. Moreover, any combination of the above-described elements in allpossible variations thereof is encompassed by the invention unlessotherwise indicated herein or otherwise clearly contradicted by context.

What is claimed is:
 1. A method for operating a time-sensitive network,TSN, comprising: providing the TSN, the TSN comprising at least a first,high-importance segment and a second, low-importance segment, whereintraffic within the first segment and traffic within the second segmentpasses through different sets of physical links in the TSN, the firstsegment being connected to a first port of a border network element thatconnects the first and second segments, and the second segment beingconnected to a second port of the border network element; remapping, onthe border network element, using a TSN per-port priority regeneration,priority labels attached to data streams received on the first port andthe second port to updated priority labels, wherein no data streamoriginally received on the first port has a same updated priority labelas any data stream originally received on the second port; splitting, onthe border network element, the data streams into a “preempting” classand a “preemptable” class based on a mapping from updated prioritylabels to classes; and forwarding the data streams from the bordernetwork element to at least one next-hop network element, wherein, whencongestion is present on a link to the next-hop network element, theforwarding of “preempting” data streams takes precedence over theforwarding of “preemptable” data streams.
 2. The method of claim 1,further comprising restoring, by the next-hop network element, theoriginal priority labels of the data streams.
 3. The method of claim 1,further comprising: splitting, on network elements in the first andsecond segments, data streams into a “preempting” class and a“preemptable” class based on a mapping from priority labels attached tothese data streams to classes; and forwarding the data streams torespective next-hop network elements wherein, at least when congestionis present on a link to the respective next-hop network element, theforwarding of “preempting” data streams takes precedence over theforwarding of “preemptable” data streams, wherein the mapping frompriority labels to classes differs between the first and secondsegments.
 4. The method of claim 3, wherein the mapping between prioritylabels and classes within the first and/or second network segments, theremapping of priority labels on the border network element, and themapping from updated priority labels to classes on the border networkelement, are coordinated such that no data stream that is in the“preemptable” class within the first and/or second network segments isin the “preempting” class upon forwarding from the border networkelement.
 5. The method of claim 3, wherein the mapping between prioritylabels and classes within the first and/or second network segments, theremapping of priority labels on the border network element, and themapping from updated priority labels to classes on the border networkelement, are coordinated such that at least one system-important datastream is in the “preempting” class both within the first and/or secondnetwork segments and upon forwarding from the border network element. 6.The method of claim 1, wherein the TSN further includes controllers,sensors and actuators of a distributed control system, DCS, for anindustrial plant as participants.
 7. The method of claim 5, wherein atleast one data stream that is part of a closed feedback loop of anindustrial process being executed on the industrial plant is chosen as asystem-important data stream.
 8. The method of claim 1, furthercomprising allocating, on the border network element, memory for queuingof frames of received data streams such that queues for frames of“preemptable” data streams accommodate more frames than queues forframes of “preempting” data streams.
 9. The method of claim 8, furthercomprising sizing the queues based on the updated priority labels of thedata streams.
 10. A method for configuring a time sensitive network,TSN, comprising: utilizing a TSN, the TSN comprising a plurality ofnetwork elements that are interconnected by links, wherein the pluralityof network elements is configured to forward data streams to respectivenext-hop network elements; identifying at least one segment of the TSNthat provides connectivity to or from at least a first further segmentand a second further segment of the TSN as a congestion-prone segment;identifying a network element that is connected to the first furthersegment by a first port, to the second further segment by a second port,and to the congestion-prone segment by a third port, as a border networkelement; and configuring the border network element to: remap, using TSNper-port priority regeneration, priority labels attached to data streamsreceived on the first port and the second port to updated prioritylabels, such that no data stream originally received on the first porthas a same updated priority label as any data stream originally receivedon the second port; split the data streams into a “preempting” class anda “preemptable” class based on a mapping from updated priority labels toclasses; and forward the data streams received on the first port and thesecond port to the third port, wherein the forwarding of “preempting”data streams takes precedence over the forwarding of “preemptable” datastreams.
 11. The method of claim 10, further comprising monitoringand/or simulating at least one key performance indicator of the TSN; andoptimizing the remapping of the priority labels, and/or the splitting ofthe data streams into the “preempting” class and the “preemptable”class, with the goal of improving the key performance indicator.
 12. Themethod of claim 11, wherein the key performance indicator comprises oneor more of: a data throughput in the congestion-prone network segment; alatency of delivery of at least one data stream; a rate of frame loss ofat least one data stream; and a measure for determinism of delivery ofat least one data stream.